Abstract
We have cloned a 4-kb region encompassing the Cu,Zn superoxide dismutase (Sod) gene from a genomic library of the Mediterranean fruit fly, Ceratitis capitata, using a cDNA probe from Drosophila melanogaster. The coding sequence of 462 bases is equally as long as that in Drosophila species. The rate of amino acid replacement over the past 100 million years is approximately the same in the Diptera and in mammals, thus excluding the hypothesis (proposed to account for an apparent acceleration in rate of evolution of Sod over geological time) that the evolution of the SOD protein is much higher in the mammals than in other organisms. The coding region is interrupted by two introns in Ceratitis, whereas only one occurs in Drosophila. Phylogenetic comparisons indicate that the second intron was present in the common dipteran ancestor, but was lost shortly after the divergence of the Drosophila lineage from other Diptera. Analysis of the exon/intron structure of Sod in various animal phyla, plants, and fungi indicates that intron insertions as well as deletions have occurred in the evolution of the Sod gene.
Highlights
The superoxide dismutases (SOD) are abundant enzymes in aerobic organisms, with highly specific superoxide dismutation activity that protects the cell against the harmfulness of free oxygen radicals (Fridovich, 1986)
Nucleotide sequence data from this article have been deposited with the GenBank Data Library under Accession No M76975
The phylogenetic divergence of these two families is dated about 80 million years ago, which corresponds to the radiation of modern mammal families, for which the possibility of a greatly accelerated rate of SOD evolution has been raised (Ayala, 1986)
Summary
The superoxide dismutases (SOD) are abundant enzymes in aerobic organisms, with highly specific superoxide dismutation activity that protects the cell against the harmfulness of free oxygen radicals (Fridovich, 1986). These enzymes have active centers that contain either iron or manganese, or both copper and zinc (Fridovich, 1986). The amino acid sequence is known in many organisms, plant, animals, fungi, and bacteria (Kwiatowski et al, I991a). The amino acids essential for catalytic action (Tainer et al, 1983), as well as those for protein structure, are strongly conserved (Getzoff et al, 1989). The phylogenetic divergence of these two families is dated about 80 million years (my) ago, which corresponds to the radiation of modern mammal families, for which the possibility of a greatly accelerated rate of SOD evolution has been raised (Ayala, 1986)
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